The present invention relates to a service device and method for applying an air blast to a broken yarn end in a ring spinning machine with a force for separating the yarn end from the previously wound yarn windings at the spinning position, and more particularly to such a service device and method in which the separating force is automatically set in relation to the extent of the build-up of previously wound windings at the spinning position.
Service devices for ring spinning machines are known for providing a blow-off device for separating a broken yarn end from the windings at a spinning position of the ring spinning machine. Such devices move along the spinning machine and automatically stop at spinning positions at which a yarn has broken and guide a blow-off nozzle in relation to the ring rail of the spinning position for directing an air blast onto the windings that separates the broken end from the windings with the aid of a compressed air source connected to the nozzle. The separated yarn end is taken up, for example, by a suction bell and processed further by the service device.
It was found that during the operation of the known service devices, the air blast is difficult to dose and the broken yarn end is not always separated from the winding in the manner desired. If the air blast is too strong, loops can be separated form the windings with the yarn end and, if the air current is too weak, no separation of the yarn end from the winding may occur.